I just realized, we actually don't know all that much about Runa do we? Like, she shares the sentiment to separate life from job with Yuki despite working in such industry, but it seems that Runa doesn't have a clear reason to do it?
Yuki brickwalled her heart due to abusive household, so her motivation to reject all romantic advances no matter how sincere is clear as day. But why should Runa do the same?